It is known that the engine braking power of a vehicle can be increased with the aid of a device or the above described type, by means of which the engine combustion chambers in brake mode during the latter portion of the compression stroke is connected to the exhaust system, for example by opening the regular exhaust valve. The result will be that the air compressed during the compression stroke flows out of the cylinders and that the compression work carried out during the compression stroke will not be recovered during the expansion stroke, and this will result in an increase in the engine braking power. An additional increase in the braking power can be achieved in this case in a known manner by connecting the exhaust system to the cylinders during the latter portion of the induction stroke, so that gas from the exhaust system can flow into the cylinders. This results in an increase in pressure in the cylinder and an inner charging so that the compression work after breaking off the communication between the cylinders and the exhaust system will be increased.
In a device known by SE-A-9401059 of the type described by way of introduction, said valve means are formed of an exhaust pressure regulator (EP regulator), i.e. a damper in the exhaust line downstream of the turbine portion of the turbocompressor unit. By varying the degree of opening of the damper, the driver can control the degree of inner charging and thus increase or reduce the braking power. The damper is controlled by a control unit into which the driver feeds a desired value of the vehicle retardation and into which engine data is fed via sensors such as the degree vehicle retardation and into which engine data is fed via sensors such as the degree of charge and the rpm, and vehicle data such as vehicle speed, accelerator position and clutch pedal position.